After a two-month period, the pieces of carpet were removed and there were duct tape adhesive marks left on the new carpet.

What is the best procedure for removing these stains from the carpet?

The answer:

There are adhesive removers made especially for this task.

You can purchase them at your local sanitary supplier, specialty carpet cleaning supply store or at a hardware stone in the paint department. One tape manufacturer recommends ...— Lynn E. Krafft, ICAN/ATEX editor